Brain Facts:
Neurons

Whenever you learn something new, that knowledge enhances the number and complexity of the brain’s neuronal networks. The result is an increase in brainpower.

Richard RestakMozart’s Brain and the Fighter Pilot
p. 52

Brain Wiring

What really matters as you age is not the size of your brain or how many neurons are left, buy how it is wired and what you can do to preserve or rejuvenate the wiring if necessary.

Jean CarperYour Miracle Brain
p.14

Methyl Molecule

The methyl molecule not only turns genes on or off but also tones down or speeds up their activity. Methyl activity likewise helps determine where in the brain the more than 100 billion neurons end up, and which other neurons their ten thousand connections will link to. The methyl molecule sculpts the body, including the brain.

Daniel Goleman, PhD, Social Intelligence
p. 150

MHC Class I Molecules

Several years ago, researchers at Harvard Medical School made the unexpected discovery that neurons have major histocompatibility complex (MHC) class I molecules on their cell surface. MHC class I molecules play a central role in a healthy, functioning immune system by helping the body recognize and destroy disease-infected cells.

"We were amazed by this finding," says Carla Shatz, PhD, now at Stanford University. "Previously it had been thought that neurons were the only cells in the body that didn't express these molecules."

When Shatz and her colleagues studied mouse models that lack MHC class I, they found another surprise: greater-than-normal strengthening of the synapses between neurons. This observation suggests that MHC class I acts as a kind of "molecular brake" on synaptic plasticity, the ability of brain cells to rewire themselves. Such plasticity is essential to learning and memory.

In mice, the "brake" for the gene encoding MHC class I appear to be released twice: during early development and again in old age. Interestingly, late in life, the gene's neural expression occurs primarily in the hippocampus and other areas of the brain involved in learning and memory.

"MHC class I neurons may also play a role in age-related neurodegenerative diseases, such as Alzheimer's and Parkinson's," says Shatz. "It may mistakenly signal the immune system to attack brain cells, just as it triggers a similar attack on the joints in cases of rheumatoid arthritis."

Researchers at the Karolinska Institute in Stockholm, Sweden, have found that removal of synapses from damaged neurons after a motor nerve injury, a process known as "synaptic stripping," is much stronger in mice that lack functioning MHC class I molecules. They also found that such mice are less likely to experience a regeneration of their motor neurons and that their glial cells react differently to the damaged neurons than do those of mice with functioning MHC class I molecules.

"These results provide a surprising link between neuroscience and immunology," says Staffan Cullheim, MD, PhD. They also mark the first time a family of molecules has been linked directly to how the cell body of a neuron reacts after its axon — the long projection that conducts electrical signals away from the cell's body — has been injured.

In earlier studies, Cullheim and other scientists had reported that MHC class I molecules can be found in particularly high levels among motor neurons in the brain stem and the spinal cord, especially after the neurons have been damaged. In his most recent study, Cullheim found that the presence of MHC class I help retain certain inhibitory synapses on the surface of injured motor neurons, thus reducing the likelihood that the neurons will fire a nerve impulse, or action potential, to neighboring cells.

The consequences of the effects of MHC class I is still not clear," says Cullheim, "but it may be linked with the ability of motor neurons to produce new axons. Mice with peripheral nerve lesions in their hind limbs exhibit less axonal bridging on those lesions when their MCH class I function is impaired."

High levels of MHC class I, on the other hand, may pose a danger to neurons in the same way as is seen for other cell types — during viral infection, for example. These high levels may even be involved in the development of neurodegenerative diseases. Research has shown that motor neurons involved in ALS and dopaminergic neurons involved in Parkinson's disease express among the largest amounts of MHC class I molecules in the nervous system.

At the University of California, San Diego, Lisa Boulanger, PhD, and her colleagues have found that changes in the levels of specific immune molecules, members of the MHC class I family, are sufficient to cause cellular and behavioral symptoms of autism and schizophrenia in mice.

If we concentrate on the number of possible neuronal connections (circuits) within the brain, we get an even more astounding number: 10 followed by a million zeros.

Richard RestakMozart’s Brain and the Fighter Pilot
p. 20

Neuron
—External Experience

There are as many neurons in a typical brain as there are stars in a galaxy. That’s amazing and sometimes really weird. There is a region in some people’s brains that responds only to pictures of Jennifer Aniston or to pictures of Halle Berry. For some people, parts of their brain light up only when they are presented with an image of Bill Clinton. Those experiments have actually been done! The brain turns out to be so sensitive to external experiences that you can literally rewire it through exposure to cultural influences.

John J. Medina
Harvard Business Review: The Science of Thinking Smarter
May 2008

Neurons

The neurons are responsible for the communication of information throughout the brain.

Richard RestakMozart’s Brain and the Fighter Pilot
p. 19

Neurons

The brain is made up of one hundred billion neurons of various types that chat with one another by way of hundreds of different chemicals, to govern our every thought and action. Each brain cell might receive input from a hundred thousand others before firing off its own signal.

John Ratey, MDSpark
p. 36

Neurons

Nerve cells called neurons carry information throughout your body. Some neurons are three feet long, and most of them live as long as you do (in contrast to other cells that die and are renewed). The neurons are separated by microscopically tiny gaps called synapses. Each neuron can communicate with hundreds of thousands of other neurons by releasing neurotransmitters – chemicals to carry messages over the synaptic gap—or by a minute electrical impulse.

Judith HorstmanThe Scientific American Day in the Life of Your Brain
p. 6

Neurons

Each neuron receives information from as many as one thousand other neurons by way of contact on one of its dendrites. The mechanism for transporting outgoing information to another cell involves the axon, a single process that extends outward for varying lengths until reaching its end point, the nerve terminal By convention, two communicating neurons are referred to as presynaptic (the message carrier) and postsynaptic (the message receiver), with any two communicating cells separated from each other by a tiny space, the synapse.

Richard RestakMozart’s Brain and the Fighter Pilot p. 26

Neuron Adaption

Most exciting is the finding that your brain is teaching old neurons new tricks and even making new neurons. When some sections of the brain go dark, other parts of the brain can learn to take over part of those functions.

Judith HorstmanThe Scientific American Day in the Life of Your Brain
p. 2

Neurons
—Communication

The communication between neurons takes place via a number of different chemical substances called neurotransmitters, and different neurotransmitters define, in effect, different networks of neurons in the brain. Techniques have been developed to identify specific neurotransmitters and, through them, “map” different neural pathways in the brain.

The other thing that helps neuron networks get stronger and become larger and more complex is emotion. There are recent experiments which show that such changes in networks can be generated simply by triggering neurons to dump "emotion chemicals" on the firing networks. These chemicals are things like adrenaline, serotonin, and dopamine, and they are delivered to specific parts of the brain by specific neuron pathways. Thus, the concomitant frequent firing and exposure to the chemicals of emotion lead to great change in neuronal networks.

James ZullThe Art of Changing the Brain

Neurons
—Habituation

Neuroscience has shown us two key things that lead to change in networks of neurons. The first one of these is simply practice. Neurons that fires a lot tend to form more connections and strengthen new connections. This is nothing new, of course, but it is more subtle than just drill, drill, drill. For example, neurons have the ability to just stop firing when the stimulus turns out to be unimportant. This phenomenon is known as habituation, and it is the same thing that happens when we stop hearing the cars that go by our window on a busy street. In fact, if you live on such a street, you eventually may come to believe that it isn't very busy at all, because you never hear the cars. So repeating isn't necessarily enough.

James ZullThe Art of Changing the Brain

Neurons
—Metabolic Process

The metabolic processes of neurons require that blood bring oxygen and glucose to brain tissue and remove waste products. Thus, measurements of blood flow as well as differences in the metabolism of specific nutrients can provide useful measures of macroscopic brain activity in each hemisphere or within smaller regions of the brain.

In addition to determining what connections are preserved, our relationships help shape our brain by guiding the connections made by new neurons. Here to old assumptions in neuroscience crumble…In fact, we know that the brain and spinal cord contain stem cells that turn into new neurons at the rate of thousands a day. The pace of neuron creation peaks during childhood but continues into old age.

Daniel Goleman, PhDSocial Intelligence
p. 157

Neurons
—New

Once a new neuron has come into being, it migrates to its position in the brain and, over the course of a month, develops to the point where it make about ten thousand connections to other neurons dispersed throughout the brain. Over the next four months or so, the neuron refines its connections; once these pathways are linked, they are locked in. As neuroscientist like to say. Cell that fire together wire together.

Daniel Goleman, PhDSocial Intelligence
p. 157

Nutrients
—Synapses, Dendrites and Receptors

You can create more connections—synapses, dendrites and receptors—through diet, supplements, and mental and physical activity.

Jean CarperYour Miracle Brain
p. 6

Orbitofrontal Cortex (OFC)

The OFC connects directly, neuron to neuron, three major regions of the brain: the cortex (or “thinking brain”), the amygdala (the trigger point for many emotional reactions), and the brain stem (the “reptilian” zones for automatic response). This tight connection suggests a rapid and powerful linkage, one that facilitates instantaneous coordination of thought, feeling, and action.

Daniel Goleman, PhD, Social Intelligence
p. 64

Spindle Cell

A newly discovered class of neuron, the spindle cell, acts the most rapidly of any, guiding snap social decisions for us and has proven to be more plentiful in the human brain than in any other species.

Daniel Goleman, PhDSocial Intelligence
p. 9

Spindle Cells Judgment

When we make an instantaneous judgment, we depend to a large extent on the operation of an unusual set of neurons: brain cells shaped like a spindle, with a large bulb at one end and a long, thick extension. Spindle cells, neuroscientists now suspect, are the secret of the speed of social intuition. They put the “snap” in snap judgment.

Daniel Goleman, PhDSocial Intelligence
p. 66

Stimulation

The brain responds to stimulation differently as we get older. In the first few years of life, the brain forms its circuits by attrition. Those neurons that are recruited into the networks and ‘nerve nets” survive, while cells not so selected die off. Thus, the sheer number of nerve cells decreases, but the richness and complexity of brain circuitry increases. The process has been compared to the art of the stone sculpture: creation via elimination rather than, as with the painter, creation via the additional materials. As we mature beyond that stage, brain cell attrition largely ceases. Instead, neurons bank together into networks that increase in number, with any one neuron potentially involved in thousands of circuits. The greater number of circuits a neuron participates in the better, because while activity and use is invigorating, the absence of activity and disuse leads to stagnation and death.

Richard RestakMozart’s Brain and the Fighter Pilot
p. 43

Synapse

The junction between cell branches is the synapse…. The synapse don’t actually touch, which is a little confusing because neuroscientist talk about synapses “wiring together” when they establish a connection. The way it works is that an electrical signal shoots down the axon, the outgoing branch, until it reaches the synapse, where a neurotransmitter carries the message across the synaptic gap in chemical form.

John Ratey, MDSpark
p. 36

Synapses
—Communication

Synapses are the essential component of communication in your brain. Your thought patterns, basic abilities and functions, and individuality are determined by how strong these synapses are, how many of them you have, and where they are. Just as connections in computers mostly connect internal components of the computer with one another, neurons mostly use synapses to talk to each other with in the brain. Only a small fraction of axons form their synapses outside the brain or spinal cord, sending signals to other organs of the body, including the muscles.

Sandra Aamodt, PhD and Sam Wang, PhDWelcome to Your Brain: Why You Lose our Car Keys but Never Forget How to Drive and Other Puzzles of Everyday Life
p. 19

Synapses
—Injury

Synapses join neurons together so tightly that no blow, short of a totally destructive injury, would ever “loosen” them.

Sandra Aamodt, PhD and Sam Wang, PhDWelcome to Your Brain: Why You Lose our Car Keys but Never Forget How to Drive and Other Puzzles of Everyday Life
p. 13

Synapses
—Size

Synapses are very small. The dendritic tree of a typical neuron is about two-tenths of a millimeter wide. Yet it receives up to two hundred thousand synaptic inputs from other neurons. Indeed, a cubic millimeter of your brain contains as many as a billion synapses. Individual synapses are so small that they contain barely enough machinery to function and are unreliable, so that arriving spikes often fail to cause any release of neurotransmitter at all.

Sandra Aamodt, PhD and Sam Wang, PhDWelcome to Your Brain: Why You Lose our Car Keys but Never Forget How to Drive and Other Puzzles of Everyday Life
p. 19

Vision

Vision begins in the eye, which is set up like a camera. A lens in the front of the eye focuses light onto a thin sheet of neurons in the back, called the retina. Retinal neurons are arranged like a sheet of pixels, each of which detects the intensity of light in a certain region of the visual world.

The retina transforms the three-dimensional world into a pattern of activity in a two-dimensional sheet of neurons, throwing away a lot of information that’s out there.

Sandra Aamodt, PhD and Sam Wang, PhDWelcome to Your Brain: Why You Lose our Car Keys but Never Forget How to Drive and Other Puzzles of Everyday Life
p. 42